Qsiprep coherence index

1

Hi,
I was wondering if someone can point to me how QSiprep processes the data which results in an increase of the coherence index? I have processed some of the DWI with QSIprep and I noticed a clear difference in coherence index of the raw and processed images. Here is the plot that shows the difference.

coherence index_UI
coherence index_UI720×576 16.2 KB

Any thoughts on what is happening under the hood?

Thanks!